Document Detail

Fluid replacement during marathon running.
MedLine Citation:
PMID:  14501315     Owner:  NLM     Status:  MEDLINE    
During endurance exercise, about 75% of the energy produced from metabolism is in the form of heat, which cannot accumulate. The remaining 25% of energy available can be used for movement. As running pace increases, the rate of heat production increases. Also, the larger one's body mass, the greater the heat production at a particular pace. Sweat evaporation provides the primary cooling mechanism for the body, and for this reason athletes are encouraged to drink fluids to ensure continued fluid availability for evaporation and circulatory flow to the tissues. Elite level runners could be in danger of heat illness if they race too quickly in hot/humid conditions and may collapse at the end of their event. Most marathon races are scheduled at cooler times of the year or day, however, so that heat loss to the environment is adequate. Typically, this postrace collapse is due simply to postural hypotension from decreased skeletal muscle massage of the venous return circulation to the heart on stopping. Elite athletes manage adequate hydration by ingesting about 200-800 mL/hour, and such collapse is rare. Athletes "back in the pack" are moving at a much slower pace, however, with heat accumulation unlikely and drinking much easier to manage. They are often urged to drink "as much as tolerable," ostensibly to prevent dehydration from their hours out on the race course. Excessive drinking among these participants can lead to hyponatremia severe enough to cause fatalities. A more reasonable approach is to urge these participants not to drink as much as possible but to drink ad libitum (according to the dictates of thirst) no more than 400-800 mL/hour.
Tim Noakes;
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Publication Detail:
Type:  Guideline; Journal Article; Practice Guideline    
Journal Detail:
Title:  Clinical journal of sport medicine : official journal of the Canadian Academy of Sport Medicine     Volume:  13     ISSN:  1050-642X     ISO Abbreviation:  Clin J Sport Med     Publication Date:  2003 Sep 
Date Detail:
Created Date:  2003-09-22     Completed Date:  2004-03-15     Revised Date:  2004-11-17    
Medline Journal Info:
Nlm Unique ID:  9103300     Medline TA:  Clin J Sport Med     Country:  United States    
Other Details:
Languages:  eng     Pagination:  309-18     Citation Subset:  IM    
The MRC/UCT Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town, South Africa.
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MeSH Terms
Fluid Therapy / methods*,  standards*
Heat Stress Disorders / diagnosis,  physiopathology,  prevention & control
Physical Endurance / physiology*
Running / physiology*
Sports Medicine / organization & administration*,  standards*
Comment In:
Clin J Sport Med. 2004 Jul;14(4):248; author reply 248-50   [PMID:  15273534 ]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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